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Date: Wed, 7 Dec 2011 22:20:43 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: linux-kernel@...r.kernel.org
Subject: [3.2-rc4 x86] (Compiler bug?) Uninitialized variable in ioapic_read_entry()
Regarding commit e57253a8 "x86, ioapic: Restore the mask bit correctly in
eoi_ioapic_irq()", I got below warning:
arch/x86/kernel/apic/io_apic.c: In function 'ioapic_read_entry':
arch/x86/kernel/apic/io_apic.c:385: warning: 'eu' is used uninitialized in this function
369: union entry_union {
370: struct { u32 w1, w2; };
371: struct IO_APIC_route_entry entry;
372: };
373:
374: static struct IO_APIC_route_entry __ioapic_read_entry(int apic, int pin)
375: {
376: union entry_union eu;
377:
378: eu.w1 = io_apic_read(apic, 0x10 + 2 * pin);
379: eu.w2 = io_apic_read(apic, 0x11 + 2 * pin);
380: return eu.entry;
381: }
382:
383: static struct IO_APIC_route_entry ioapic_read_entry(int apic, int pin)
384: {
385: union entry_union eu;
386: unsigned long flags;
387: raw_spin_lock_irqsave(&ioapic_lock, flags);
388: eu.entry = __ioapic_read_entry(apic, pin);
389: raw_spin_unlock_irqrestore(&ioapic_lock, flags);
390: return eu.entry;
391: }
I compared using several gcc versions.
It turned out that only gcc 4.4 shows this warning.
--- gcc (SUSE Linux) 4.6.2 in OpenSUSE 12.1 ---
CC arch/x86/kernel/apic/io_apic.o
--- gcc (GCC) 4.5.1 20100924 (Red Hat 4.5.1-4) on Fedora 14 ---
CC arch/x86/kernel/apic/io_apic.o
--- gcc (Debian 4.4.5-8) 4.4.5 on Debian Squeeze ---
CC arch/x86/kernel/apic/io_apic.o
arch/x86/kernel/apic/io_apic.c: In function ‘ioapic_read_entry’:
arch/x86/kernel/apic/io_apic.c:385: warning: ‘eu’ is used uninitialized in this function
--- gcc (Ubuntu 4.4.3-4ubuntu5) 4.4.3 on Ubuntu 10.04 ---
CC arch/x86/kernel/apic/io_apic.o
arch/x86/kernel/apic/io_apic.c: In function ‘ioapic_read_entry’:
arch/x86/kernel/apic/io_apic.c:385: warning: ‘eu’ is used uninitialized in this function
--- gcc (Debian 4.3.2-1.1) 4.3.2 on Debian Lenny ---
CC arch/x86/kernel/apic/io_apic.o
--- gcc (GCC) 4.2.4 (Ubuntu 4.2.4-1ubuntu4) on Ubuntu 8.04 ---
CC arch/x86/kernel/apic/io_apic.o
--- gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-51) on CentOS 5 ---
CC arch/x86/kernel/apic/io_apic.o
--- gcc (GCC) 3.3.5 (Debian 1:3.3.5-13) on Debian Sarge ---
CC arch/x86/kernel/apic/io_apic.o
arch/x86/kernel/apic/io_apic.c: In function `setup_ir_ioapic_entry':
arch/x86/kernel/apic/io_apic.c:1354: warning: unsigned int format, different type arg (arg 11)
It turned out that gcc 4.3 and 4.5 do not inline __ioapic_read_entry() whereas
gcc 4.4 inlines __ioapic_read_entry().
--- gcc (Debian 4.3.2-1.1) 4.3.2 on Debian Lenny ---
00000040 <__ioapic_read_entry>:
40: 56 push %esi
41: 53 push %ebx
42: 8d 58 05 lea 0x5(%eax),%ebx
45: 8d 04 80 lea (%eax,%eax,4),%eax
48: 8b 0c c5 ac 08 00 00 mov 0x8ac(,%eax,8),%ecx
4f: c1 e3 0c shl $0xc,%ebx
52: 8d 74 12 10 lea 0x10(%edx,%edx,1),%esi
56: 81 e1 ff 0f 00 00 and $0xfff,%ecx
5c: 03 0d 00 00 00 00 add 0x0,%ecx
62: 29 d9 sub %ebx,%ecx
64: 89 31 mov %esi,(%ecx)
66: 83 c1 10 add $0x10,%ecx
69: 8b 09 mov (%ecx),%ecx
6b: 8b 04 c5 ac 08 00 00 mov 0x8ac(,%eax,8),%eax
72: 8d 54 12 11 lea 0x11(%edx,%edx,1),%edx
76: 25 ff 0f 00 00 and $0xfff,%eax
7b: 03 05 00 00 00 00 add 0x0,%eax
81: 29 d8 sub %ebx,%eax
83: 89 10 mov %edx,(%eax)
85: 83 c0 10 add $0x10,%eax
88: 8b 10 mov (%eax),%edx
8a: 89 c8 mov %ecx,%eax
8c: 5b pop %ebx
8d: 5e pop %esi
8e: c3 ret
8f: 90 nop
000004e0 <ioapic_read_entry>:
4e0: 83 ec 0c sub $0xc,%esp
4e3: 89 74 24 04 mov %esi,0x4(%esp)
4e7: 89 c6 mov %eax,%esi
4e9: b8 4e 08 00 00 mov $0x84e,%eax
4ee: 89 1c 24 mov %ebx,(%esp)
4f1: 89 d3 mov %edx,%ebx
4f3: 89 7c 24 08 mov %edi,0x8(%esp)
4f7: e8 fc ff ff ff call 4f8 <ioapic_read_entry+0x18>
4fc: 89 da mov %ebx,%edx
4fe: 89 c7 mov %eax,%edi
500: 89 f0 mov %esi,%eax
502: e8 39 fb ff ff call 40 <__ioapic_read_entry>
507: 89 c6 mov %eax,%esi
509: 89 d3 mov %edx,%ebx
50b: b8 4e 08 00 00 mov $0x84e,%eax
510: 89 fa mov %edi,%edx
512: e8 fc ff ff ff call 513 <ioapic_read_entry+0x33>
517: 89 f0 mov %esi,%eax
519: 89 da mov %ebx,%edx
51b: 8b 1c 24 mov (%esp),%ebx
51e: 8b 74 24 04 mov 0x4(%esp),%esi
522: 8b 7c 24 08 mov 0x8(%esp),%edi
526: 83 c4 0c add $0xc,%esp
529: c3 ret
52a: 8d b6 00 00 00 00 lea 0x0(%esi),%esi
--- gcc (Ubuntu 4.4.3-4ubuntu5) 4.4.3 on Ubuntu 10.04 ---
00001d60 <ioapic_read_entry>:
1d60: 83 ec 0c sub $0xc,%esp
1d63: 89 1c 24 mov %ebx,(%esp)
1d66: 89 c3 mov %eax,%ebx
1d68: b8 4e 08 00 00 mov $0x84e,%eax
1d6d: 89 74 24 04 mov %esi,0x4(%esp)
1d71: 89 7c 24 08 mov %edi,0x8(%esp)
1d75: 89 d7 mov %edx,%edi
1d77: e8 fc ff ff ff call 1d78 <ioapic_read_entry+0x18>
1d7c: 8d 53 05 lea 0x5(%ebx),%edx
1d7f: 8d 1c 9b lea (%ebx,%ebx,4),%ebx
1d82: 8b 0c dd ac 08 00 00 mov 0x8ac(,%ebx,8),%ecx
1d89: c1 e2 0c shl $0xc,%edx
1d8c: 8d 74 3f 10 lea 0x10(%edi,%edi,1),%esi
1d90: 81 e1 ff 0f 00 00 and $0xfff,%ecx
1d96: 03 0d 00 00 00 00 add 0x0,%ecx
1d9c: 29 d1 sub %edx,%ecx
1d9e: 89 31 mov %esi,(%ecx)
1da0: 8b 71 10 mov 0x10(%ecx),%esi
1da3: 8b 0c dd ac 08 00 00 mov 0x8ac(,%ebx,8),%ecx
1daa: 8d 7c 3f 11 lea 0x11(%edi,%edi,1),%edi
1dae: 81 e1 ff 0f 00 00 and $0xfff,%ecx
1db4: 03 0d 00 00 00 00 add 0x0,%ecx
1dba: 29 d1 sub %edx,%ecx
1dbc: 89 39 mov %edi,(%ecx)
1dbe: 8b 59 10 mov 0x10(%ecx),%ebx
1dc1: 89 c2 mov %eax,%edx
1dc3: b8 4e 08 00 00 mov $0x84e,%eax
1dc8: e8 fc ff ff ff call 1dc9 <ioapic_read_entry+0x69>
1dcd: 89 f0 mov %esi,%eax
1dcf: 89 da mov %ebx,%edx
1dd1: 8b 1c 24 mov (%esp),%ebx
1dd4: 8b 74 24 04 mov 0x4(%esp),%esi
1dd8: 8b 7c 24 08 mov 0x8(%esp),%edi
1ddc: 83 c4 0c add $0xc,%esp
1ddf: c3 ret
--- gcc (GCC) 4.5.1 20100924 (Red Hat 4.5.1-4) on Fedora 14 ---
00000020 <__ioapic_read_entry>:
20: 56 push %esi
21: 8d 48 05 lea 0x5(%eax),%ecx
24: 8d 04 80 lea (%eax,%eax,4),%eax
27: 53 push %ebx
28: 8d 1c c5 60 08 00 00 lea 0x860(,%eax,8),%ebx
2f: 8b 43 0c mov 0xc(%ebx),%eax
32: c1 e1 0c shl $0xc,%ecx
35: 8d 74 12 10 lea 0x10(%edx,%edx,1),%esi
39: 25 ff 0f 00 00 and $0xfff,%eax
3e: 03 05 00 00 00 00 add 0x0,%eax
44: 29 c8 sub %ecx,%eax
46: 89 30 mov %esi,(%eax)
48: 8b 40 10 mov 0x10(%eax),%eax
4b: 8d 74 12 11 lea 0x11(%edx,%edx,1),%esi
4f: 8b 53 0c mov 0xc(%ebx),%edx
52: 81 e2 ff 0f 00 00 and $0xfff,%edx
58: 03 15 00 00 00 00 add 0x0,%edx
5e: 29 ca sub %ecx,%edx
60: 89 32 mov %esi,(%edx)
62: 8b 52 10 mov 0x10(%edx),%edx
65: 5b pop %ebx
66: 5e pop %esi
67: c3 ret
68: 90 nop
69: 8d b4 26 00 00 00 00 lea 0x0(%esi,%eiz,1),%esi
00000200 <ioapic_read_entry>:
200: 83 ec 0c sub $0xc,%esp
203: 89 1c 24 mov %ebx,(%esp)
206: 89 c3 mov %eax,%ebx
208: b8 62 12 00 00 mov $0x1262,%eax
20d: 89 74 24 04 mov %esi,0x4(%esp)
211: 89 d6 mov %edx,%esi
213: 89 7c 24 08 mov %edi,0x8(%esp)
217: e8 fc ff ff ff call 218 <ioapic_read_entry+0x18>
21c: 89 f2 mov %esi,%edx
21e: 89 c7 mov %eax,%edi
220: 89 d8 mov %ebx,%eax
222: e8 f9 fd ff ff call 20 <__ioapic_read_entry>
227: 89 c3 mov %eax,%ebx
229: 89 d6 mov %edx,%esi
22b: b8 62 12 00 00 mov $0x1262,%eax
230: 89 fa mov %edi,%edx
232: e8 fc ff ff ff call 233 <ioapic_read_entry+0x33>
237: 89 d8 mov %ebx,%eax
239: 89 f2 mov %esi,%edx
23b: 8b 1c 24 mov (%esp),%ebx
23e: 8b 74 24 04 mov 0x4(%esp),%esi
242: 8b 7c 24 08 mov 0x8(%esp),%edi
246: 83 c4 0c add $0xc,%esp
249: c3 ret
24a: 8d b6 00 00 00 00 lea 0x0(%esi),%esi
Also, it turned out that this warning does not apprar when compiled with
CONFIG_M586MMX and earlier. This warning appears when compiled with CONFIG_M686
and later.
I don't know whether this warning is a false positive or not.
Can somebody who understand assembly code check this?
Regards.
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